Device and method for bending pipe material

ABSTRACT

In the case of bending an outer pipe, a pressure die provided just in front of a bending section is provided with a groove, wherein the shape of the groove on the side far from the bending section is semi-circular and of which the diameter corresponds to that of the outer pipe before bending, while the shape of the groove on the side near the bending section is tapered semi-elliptically. With this, the cross-sectional shape of the outer pipe is caused to change into a substantially elliptical shape in which the outside of the section to be bent is tapered. The cross-sectional shape becomes substantially circular when bending is completed.

TECHNICAL FIELD

The present invention relates to an apparatus and technique for bending a pipe material without deforming the cross-sectional shape thereof.

BACKGROUND ART

As a technique for bending a pipe material without deforming the cross-sectional shape thereof, Japanese Unexamined Patent Publication No. 2003-145219 discloses, for example, a method for inserting a deformation preventive jig made of a rubber elastic body which is axially compressible and expandable in the radial direction within a pipe and bending the pipe in a condition in which the deformation preventive jig is axially compressed and expanded in the radial direction. Japanese Unexamined Patent Publication No. Hei 10-118719 discloses a method for bending a double pipe in which a mandrel that can expand an inner pipe into an elliptical form is inserted into the inner pipe to bend the inner pipe while deforming the inner pipe and after bending, liquid of predetermined pressure is supplied into the inner pipe to restore the inner pipe to a circular form. Japanese Unexamined Patent Publication No. Hei 8-276221 also discloses a method for bending a double pipe in which a backup material is filled in a gap between an outer pipe and an inner pipe for bending and the backup material is removed from the gap after bending.

However, in the case of a single pipe, it takes a great deal of time to insert a core material into the pipe, fill the backup material therein, or feed pressurized liquid into the pipe after bending. In addition, there are also problems that the number of man-hours or working hours increases and working efficiency is not good.

It is therefore an object of the present invention to solve the foregoing problems and provide an apparatus and method for not only reducing time and man-hours, but also to reduce working hours in a bending process for preventing deformation after bending.

DISCLOSURE OF THE INVENTION

To attain the above object, according to the present invention, a bending apparatus having a pressure die for cramping a lateral surface to be bent provided just in front of a bending section of a pipe material is provided, in which the front surface of the pressure die is longitudinally provided with a substantially semi-circular groove which can fit a substantially half body of an outer circumferential surface of the pipe material, wherein the shape of the groove on the side far from the bending section is semi-circular of which the diameter corresponds to that of the pipe material before bending, while the shape of the groove on the side near the bending section is a semi-elliptical taper.

With this pressure die, a cross-sectional shape of a bending section of a pipe material is caused to change into a substantially elliptical shape so that the outside of the section to be bent is tapered just before bending. After this, by bending the pipe material, the cross-sectional shape after bending can be made closer to a circular shape. Thus, in the case of a single pipe, it is possible to save the trouble of inserting a mandrel or a backup material into the pipe and reduce working hours.

In this case, it is desirable to confirm the specific elliptical shape before bending by conducting experiments etc. in advance because the desired shape varies delicately with, for example, the thickness or diameter of the pipe, the curvature of bending and the like.

It is to be noted that such a bending apparatus is not only applicable to bending of a single pipe, but also to bending of the outer pipe of a double pipe.

By using the bending apparatus, the cross-sectional shape of the bending section of the pipe material is caused to change into a substantially elliptical shape before bending so that the outside of the section to be bent is tapered, then bending is carried out.

Further, a process for deforming the cross-sectional shape and a process for bending can be performed by a series of operations because the pressure die is provided just in front of the bending section. Thus, the operations can be efficiently carried out.

As a groove shape of the pressure die provided just in front of the bending section, by making the shape of the groove on the side near the bending section a semi-elliptic taper, the cross-sectional shape of the pipe material changes to have a substantially tapered elliptical shape at the time of bending. As a result, the cross-sectional shape after bending can be made closer to a circular shape. Accordingly, in the case of the single pipe, it is possible to save a lot of trouble for inserting the mandrel or backup material within the pipe and reduce working hours.

Further, if the process for deforming the cross-sectional shape of the bending section and the bending process are carried out by the same bending apparatus in a series of operations, operations becomes more efficient and working hours can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a bending apparatus for use in bending according to the present invention;

FIG. 2 is an explanatory view of a pressure die;

FIG. 3 (a) is a cross-sectional view taken along the line A-A of FIG. 2 and FIG. 3 (b) is a cross-sectional view taken along the line B-B of FIG. 2;

FIG. 4 is a view of the state before bending; and

FIG. 5 is a view of the state during bending.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a schematic view of a bending apparatus used in bending according to the present invention. FIG. 2 is an explanatory view of a pressure die. FIG. 3 is a cross-sectional view of FIG. 2, wherein FIG. 3 (a) is a cross-sectional view taken along line A-A and FIG. 3 (b) is a cross-sectional view taken along line B-B. FIG. 4 is a view of the state before bending and FIG. 5 is a view of the state during bending.

A method for bending a pipe material according to the present invention is provided to secure a substantially circular shape without using a mandrel or a backup material in the case of bending a metal pipe etc. of a circular cross-section and is characterized in that the pipe is caused to deform into a substantially elliptical shape in advance before bending. In the present embodiment, the bending method is applied to bending of a double pipe.

Such a double pipe is, for example, an exhaust pipe for a motorcycle etc. In the case of the exhaust pipe, when the gap between an inner pipe and an outer pipe becomes narrower, it seriously affects the engine efficiency. When the gap of the outside of the section to be bent falls within a predetermined range, black burn whereby the lateral surface to be bent of the outer pipe changes blackens is generated and this becomes a factor for deteriorating the quality of the external appearance.

In a conventional bending method, bending is carried out, for example, by inserting a mandrel etc. into an inner pipe and also inserting a spatula mandrel etc. into a gap between an outer pipe and an inner pipe, and after bending, the spatula mandrel etc. is pulled out. In the case of the present invention, the mandrel is inserted into the inner pipe as in the past, but the spatula mandrel etc. is not inserted into the gap between the outer pipe and the inner pipe. Instead, the cross-sectional shape of the outer pipe is caused to change before bending, thereby making the cross-sectional shape of the outer pipe substantially circular at the time when the bending is finished.

Change of the cross-sectional shape of the outer pipe prior to bending is made just before bending. After changing the cross-sectional shape, bending is continuously carried out by a series of operations.

One example of a bending apparatus for bending such a double pipe as described above will now be described with reference to FIG. 1.

A bending apparatus 1 comprises a bending die 2 rotatably provided around a central axis, a rotating table 3 provided on the lateral side of the bending die 2, and a stationary table 4 provided adjacent to the rotating table 3. A fastening die 5 is provided on the rotating table 3 to face a clamping section 2 c of the bending die 2. The fastening die 5 is provided to move closer to and be detachable from the clamping section 2 c. Provided on the stationary table 4 is a pressure die 6 which can move forward or move back in the same direction as the moving direction of the fastening die 5.

The outer circumferential surface of the bending die 2 and the front surface of the clamping section 2 c are respectively provided with a substantially semi-circular groove into which an inside outer circumferential surface section corresponding to the inside section to be bent of an outer pipe can be fitted. The front surface of the fastening die 5 is also provided with a substantially semi-circular groove into which an outside outer circumferential surface section corresponding to the outside of the section of the outer pipe to be bent can be fitted.

As shown in FIG. 2, the front surface of the pressure die 6 is also provided with a groove m into which an outside outer circumferential surface section corresponding to the outside of the outer pipe to be bent can be fitted. As shown in FIG. 3, the groove m is formed to have a different shape at a section taken along the line A-A near the fastening die 2 and at a section taken along the line B-B far from the fastening die 2.

Namely, FIG. 3 (b) is a cross-sectional view of a section taken along the line B-B far from the fastening die 2. The groove width z of this section is almost the same as the diameter of an outer pipe Po before bending. The groove m is formed to have a semi-circular shape with a radius of z/2.

FIG. 3 (a) is a cross-sectional view of a section taken along the line A-A near the fastening die 2. The groove m of this section is provided in which the groove width x is made slightly smaller than the diameter of the outer pipe Po before bending and the entrance sections of both groove ends are provided with slight straight sections s from which the tapered semi-elliptical groove is formed with a depth of y longer than x/2.

The groove m at an intermediate section between the section taken along the line B-B and the section taken along the line A-A has a shape gradually changing from the semi-circular shape to the semi-elliptical shape.

A mandrel 7 which can be inserted into an inner pipe is provided toward the bending die 2. The base end section of the mandrel 7 is supported by a supporting member 8 of which the rear surface side is provided with a mandrel cylinder 9. The front section of the mandrel 7 is extendably provided toward the tangential direction of the bending die 2. The front section is extendably provided substantially until the vicinity of the lateral side of a central section of the bending die 2.

Such a resinous wiper 11 as shown in FIG. 4 is provided in front of the pressure die 6 to combat wrinkles. The front surface of the wiper 11 is also provided with a semi-circular groove.

In such a bending apparatus 1, as shown in FIG. 4, after positioning in a condition in which the mandrel 7 is inserted into an inner pipe Pi of a double pipe P, the fastening die 5 is moved forward to hold the front section of the outer pipe Po between the fastening die 5 and the clamping section 2 c of the bending die 2 for clamping, wherein the pressure die 6 is moved forward to touch an outside section of the outer pipe Po to be bent, thereby cramping the outside section to be bent.

Next, by rotating the rotating table 3 and the bending die 2 at the same time, the front end of the double pipe P is bent as shown in FIG. 5 along a radius of curvature of the bending die 2 while being clamped between the fastening die 5 and the clamping section 2 c of the bending die 2. In this case, the position periphery of the fastening die 5 and the clamping section 2 c clamping the outer pipe Po at the beginning is regarded as a bending section. However, the outer pipe Po provided on the base end side from the bending section advances within the groove m while being pressed against the groove m of the pressure die 6 by the reactive force at the time of bending. When the outer pipe Po leaves the pressure die 6, the shape of the outside semi-circular section of bending (to be bent) is formed to have a tapered semi-elliptical shape and then, bent.

As bending makes progress, the outside section of the outer pipe Po to be bent receives the force of elongation and the tapered semi-elliptical section changes to have a semi-circular shape, wherein the entire cross-sectional shape changes from a substantially elliptical shape to a substantially circular shape.

Referring to the inner pipe Pi, the entire cross-sectional shape is maintained in a substantially circular shape by the mandrel 7, but this is the same as in the conventional equipment.

Although the above-mentioned embodiments are described by taking bending of the outer pipe Po of the double pipe P as an example, but these are also applicable to bending of a single pipe.

Embodiment

In the case where the outer pipe Po 35 mm in diameter and 1.5 mm thick is bent, the groove width x of FIG. 3 (a) is set about 34 mm, the depth y is set about 19 mm, the length of the straight section s is set about 2 mm, and the radius r of the tapered front section is set about 12 mm.

When the outer pipe Po is bent using the bending die 2 with a curvature radius of 86 mm, the diameter of the outer pipe Po in the bending direction is 33.4 mm and the diameter thereof in the bending and right-angled direction is 34.8 mm. As a result, a substantially circular shape is secured.

On the contrary, in the case of a conventional bending unit in which the spatula mandrel is inserted between the outer pipe Po and the inner pipe Pi, the diameter of the outer pipe Po in the bending direction is 31.7 mm and the diameter thereof in the bending and right-angled direction is 37.6 mm. As a result, the conventional bending showed a higher degree of flatness than the present embodiment.

Further, in the conventional bending, it took 14 seconds to bend one pipe, but in the case of the present invention, it only took 7 seconds, a time reduction of 50%.

Still further, in a bending process, there was no such a problem as the lateral surface of the outer pipe Po to be bent blackens because a gap between the outer pipe Po and the inner pipe Pi of the outside section to be bent can be secured at more than a predetermined width.

With this, the effectiveness of the present invention was confirmed. Of course, it goes without saying that specific requirements of the tapered shape to be deformed must be changed in advance depending on the diameter of pipe material, the thickness thereof, the curvature of bending and the like.

It is to be understood that the present invention is not limited to the embodiments described above. Numerous modifications and variations having substantially the same construction and the same action and effect as the matters described in the claims of the present invention fall within the technical scope of the present invention.

For example, the pipe material other than the exhaust pipe can be used and the present invention can also be applied to bending of a single pipe other than a double pipe.

INDUSTRIAL APPLICABILITY

In bending a pipe material, by first changing the cross-sectional shape and then bending the pipe material, the trouble of inserting a mandrel, fillers or the like into the pipe is eliminated and working hours can be reduced. 

1. A bending apparatus having a pressure die cramping a lateral surface to be bent of a pipe material provided just in front of a bending section of the pipe material, wherein the front surface of the pressure die is longitudinally provided with a substantially semi-circular groove that can fit a substantially half body of the outer circumferential surface of the pipe material, wherein a groove shape on a side far from the bending section is semi-circular and of which the diameter corresponds to that of the pipe material before bending, while a groove shape on a side near the bending section is semi-elliptically tapered. 2-3. (canceled)
 4. The bending apparatus according to claim 1, wherein the semi-circular groove whose diameter corresponds to that of the pipe material before bending and the semi-elliptically tapered groove are provided on the pressure die continuously. 